1. Field of the Invention
The present invention relates to a flame-resistant fiber possessing excellent flame resistance and weather resistance, and a fiber molding using the same.
2. Description of the Related Art
Demand exists today for imparting flame resistance to a variety of fiber products with respect to fire prevention and safety. Fibers comprising thermoplastic resins and fiber moldings containing these fibers (hereafter referred to as ‘fiber materials’), such as nonwoven fabrics, are not exceptions. In particular, for the majority of fiber materials used in automobile interiors, interior housing materials, filters etc., flame resistance is imparted by a number of methods, such as compounding with flame-retardants and treating the fiber surface with flame-retardants. Examples of flame-retardants include halogenated compounds, heavy metal compounds, metal hydroxides, and phosphorus compounds, which may be used individually or as a mixture of two or more compounds.
Of the different flame-retardants, chlorine- or bromine-based halogen compounds and combinations of halogen compounds with antimony oxide are widely used. In particular, flame retardant compositions comprising bromine-based halogen compounds and antimony trioxide are widely used in a range of applications due to their excellent flame resistance. However, in recent years as public concerns regarding environmental issues have grown, halogen compounds have been regarded as a problem due to their release of hazardous gases (hydrogen halides) on combustion and their potential as a source of dioxins. In addition, heavy metal compounds, such as antimony oxide, have been indicated as possible carcinogenic substances. Therefore, their use in places with proximity to humans is inadvisable from a public health standpoint.
Furthermore, for fibers used in automobile interiors, interior housing materials, filters, etc., a decrease in physical strength caused by heat or UV degradation must be prevented because fibers in these applications are likely to be used over long time-spans. The compounding of weather-proofing agents into the fibers is a common method of preventing degradation. However, since the above-described halogen compounds and antimony oxide release acid components that deactivate weather-proofing agents, weather resistance of fibers containing the above-described flame-retardant compositions cannot be improved and, therefore, the fibers do not exhibit durability over long-term use. For this reason, flame-retardants that do not inhibit weather resistance, do not contain heavy metals, or do not release hazardous substances on combustion or processing are highly sought-after.
A number of flame-retardants other than halogen compounds and antimony oxide have been studied to solve the above-described problems, but an agent displaying good flame resistance equivalent to the halogen compounds and antimony oxide has not been found to date. Metal hydroxides and phosphorus compounds can also be used as a flame-retardant, but the amount required to impart the desired flame resistance to the fiber materials tends to be significantly higher than that of the above-described flame-retardants. In the manufacture of fiber materials by the spinning of thermoplastic resin compositions containing flame-retardants, increased amounts of added flame-retardants not only cause a decrease in the mechanical strength of the obtained fiber materials but also raise difficulties in the manufacturing process itself. Additionally economical problems also arise.
The use of hindered amine derivatives with specific structures as a flame-retardant which do not release hazardous substances in combustion or processing is disclosed, for example, in the patent references 1 to 4 below. However, the same problems as those described above exist because the hindered amine derivatives described in those patents display inferior flame resistance to the above-described flame-retardant compositions.
In other patents, for example, patent references 3 and 4 below using the hindered amine derivatives together with phosphorus compounds, such as aryl phosphite, are disclosed. However, similar to the flame-retardants described above, their flame resistance is insufficient. In addition, when a significant amount of aryl phosphite is used to increase flame resistance, various other problems arise, such as poor strength of the fiber materials, decrease in drawability as a result of the low boiling point aryl phosphite volatilizing at the spinning temperature, and deteriorating product quality and flame resistance due to the likelihood of aryl phosphite bleeding from the obtained fiber materials.
Further, phosphoric acid esters, such as aryl phosphite, are likely to contain residual catalysts used in the manufacture of the esters. Thus, when phosphoric acid esters are used in manufacturing fiber materials from polyolefins, the residual catalyst accelerates polyolefin degradation, resulting in a decrease in strength of the fiber materials. In addition, the characteristic odor of phosphoric acid esters not only deteriorates the working environment in which the fiber materials themselves are manufactured but also permeates into the manufactured fiber materials.
Use of specific cyclic phosphazenes as a flame-retardant is disclosed, for example, in the patent reference 5 below. The cyclic phosphazenes are easy to handle, do not cause environmental problems, and have excellent thermal stability and resistance to hydrolysis. However, using cyclic phosphazenes in isolation again has the same problem as described above due to their lower flame resistance when compared to the above-described flame-retardant compositions. Therefore, cyclic phosphazenes need to be compounded at a level in excess of 10 wt % to obtain sufficient flame resistance. Uses of thermoplastic resin compositions containing significant amounts of flame-retardants are limited to products that are thermal compression molded, and the molding of very fine products such as fiber materials from these compositions is difficult. Immersing the fiber materials into a solution containing cyclic phosphazenes is an alternative way to impart flame resistance. Nevertheless, the method only allows the cyclic phosphazenes to adhere to the surface of the fiber materials and, thus, the cyclic phosphazenes are released from the fiber materials following post-processing, post-treating, and long-term use, resulting in extremely low retention of flame-resistant properties.    Reference 1: WO 99/00450    Reference 2: JP 2001-254225A    Reference 3: JP 2002-115118A    Reference 4: US 2002/0015847A1    Reference 5: JP 2001-192392A